Adjustable color correction automated high intensity stage lights

ABSTRACT

Color correction system for an automated stage light that allows the color temperature of the light beam to be continuously adjustable to both a higher and lower Kelvin value than the natural temperature of the open beam, by filtering using a dual peak filter and also color correcting the beam.

BACKGROUND

Many automated stage light fixtures are fitted with an arc lamp which isthe source of light for the fixture. These lamps, commonly called HighIntensity Discharge (HID) sources, produce light by continuouslydischarging a plasma arc through a high pressure mixture of mercuryvapor, noble gases and the evaporated salts of rare earth elements. Whenexcited by the plasma arc, this mixture creates a small-volume lightemitter with high luminous efficiency. The color and quality of thelight emitted is primarily determined by the mixture of these elementsand is typically similar to daylight with a Correlated Color Temperature(CCT) of about 6000 Kelvins.

Often these automated luminaires are used in conjunction with otherlighting instruments in a television studio or on a film set. It thenbecomes desirable to adjust the color temperature of the HID source tomatch that of the other lighting instruments so that the different lightsources will be rendered to look the same by the film or televisioncamera. Typically the conventional lights have a tungsten filamentsource which produces light with a CCT of 3200 Kelvins. Often spotlightsand other sources are used that have other, and sometimes higher colortemperature beams. Therefore, the desired color temperature of theautomated luminaire is dependent on the particular shot the camera istaking and on the other lighting instruments used in that particularshot.

In addition to color temperature, a second and equally important qualityof the light emanating from the instrument is its Color Rendering Index(CRI). The illuminating beam's CRI is a measure of how well balanced itsspectrum is compared to that of natural daylight or more specifically,compared to a black body radiator at a similar color temperature. Lightwith a high CRI renders all colors faithfully while that with a low CRI,like poor quality fluorescent illumination, can give false impressionsof colors. Therefore having a luminaire with adjustable CCT whilemaintaining a high CRI is very beneficial as the cameras will rendertheir subjects' color faithfully. This is especially important when thesubject is human skin since we are all extremely sensitive to theappearance of skin tones. Light with a low CRI illuminating anindividual can make them look ill.

Existing adjustable color temperature correcting systems for automatedluminaires are capable of only lowering the color temperature of thelight. Furthermore, the CRI of the adjusted light usually deterioratesas the color temperature is adjusted which is inherent in the design ofthe filtration system. The filtration is typically an optical thin filmapplied to a glass wheel where a portion of the wheel intersects thelight source beam inside the luminaire.

The filter 100 is typically spatially patterned to produce a densitygradient that runs circumferentially around the wheel as shown in FIG.1A running from an open area at 110 to a low density area at 115, tohigher density areas at 120. This allows the saturation of the filtercoating to vary around the wheel. The rotational position of the wheelthen controls the color temperature of the beam exiting the luminaire.

At the beginning of the gradient, the patterning completely removes allof the filter material so it has no effect on the natural colortemperature of the beam. This is called the “open” position 110 of thefilter wheel. At the end of the gradient or “full-in”, position 130 mostor all of the filter material is left on the wheel so that the colortemperature of the filtered beam is the desired minimum CCT, usuallyaround 3000 Kelvins. In between, over the area 120 the varying densityfilter gradient causes a changing ratio between filtered and unfilteredlight passing through the wheel and therefore a change in CCT of thebeam. The changing CCT of the light beam with wheel position isillustrated in the 1933 CIE chromaticity diagram of FIG. 1B as a seriesof points connected by the dotted line. The color temperature of severalpoints along the line are noted beginning with the “open” temperature ofthe unfiltered beam of 5600K and ending with the “full-in” CCT of 2450K.

Note that the locus of filtered color correction points is straightbetween “open” 210 and “full-in” 220 indicating that a change insaturation has been caused by the filtration, the saturation of thecolor point being affected by the patterning density while the hueimparted by the filter material remains constant. Note also that the CRIof the light decreases as the locus of filtered light diverges away fromthe Planckian Locus or Black Body Curve; the Planckian Locus being thelocus of white points all having a perfect Color Rendering Index of 100.

SUMMARY

Embodiments describe a color correction system for an automated stagelight that allows the color temperature of the light beam to becontinuously adjustable to both a higher and lower Kelvin value than thenatural temperature of the open beam.

Another aspect improves the Color Rendering Index of the open beam atall color temperatures so that the light from the stage light rendersall colors accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a gradient color wheel;

FIG. 1B shows a prior art chromaticity diagram;

FIG. 2 shows a block diagram of a luminaire being controlled by acontrolling console;

FIG. 3 shows the arc spectrum of an HID lamp;

FIG. 4 shows the characteristics of the peak suppression filter usedaccording to an embodiment;

FIG. 5 shows the filtered HID arc spectrum;

FIGS. 6A and 6B respectively show the lamp side and lens side coatingaccording to the present application;

FIG. 7 shows the chromaticity diagram of a composite color correctionwheel;

FIGS. 8 and 9 respectively show transfer curves for the composite upconverter and down converter of embodiments.

DETAILED DESCRIPTION

An embodiment is shown in FIG. 2. In this embodiment, a luminaire 199 isformed with a number of parts. The light from the luminaire is createdby a High-energy discharge arc lamp 200 that produces high-energy lightwhich is focused into a beam 210 via reflector 205.

FIG. 3 shows a typical emissions spectrum produced by such an HID arclamp. Since the term HID encompasses an entire family of sources, itshould be understood that the spectra of individual lamps within thefamily vary somewhat as each lamp is designed to produce a particularcolor temperature of light and to have other special characteristics,such as a compact arc length or an extended lifetime. The design forthese performance characteristics affects the spectral energydistribution of the light produced by each lamp within the family.However all HID sources have a common signature; that of the prominentspectral peaks that result from the emissions from the excited mercuryvapor in the plasma arc. Three spectral peaks stand out above thewide-band radiation from the other elements in the plasma: a deep bluecolor peak at 435.8 nm, a blue-green peak at 546.1 nm and a yellow-greenpeak at 578.2 nm, the latter two being the most dominating.

The smallest peak at 435.8 nm has little effect on CRI as the Test ColorSamples (TCS) used to calculate the CRI value are not stronglyinfluenced by this deep blue peak and the eye response at thatwavelength is significantly diminished. The two dominant centralspectral peaks are particularly problematic however, as they contain asignificant amount of spectral energy, are centered in the middle of thephotopic curve where the human eye is most sensitive and they are not ofa particularly attractive color, especially when applied to human skin.Furthermore, television cameras and to some extent, digital or filmcinema cameras, are excessively sensitive to the peak energies in thesetwo bands. Generally, they tend to respond exceptionally to these peaks;rendering a scene with strong green and blue-green hues.

According to an embodiment, the inventor recognizes that these twocentral peaks created by the light source/lamp can be problematic forillumination, by creating colors which many may find objectionable.

FIG. 2 shows how the beam 210 is filtered through a color correctionwheel 220 described herein. This color correction wheel may reduce thesepeaks by applying a very selective and efficient multi-layer dielectricinterference filter according to embodiments, dielectric interferencefilter has different parts that are coated on different sides of thecolor correction wheel 220. FIG. 2 also shows how the filtered beam canalso be passed through other optical components, including a colorfilter array 230, of gobo 240, and a zoom lens 250. All of these partsare controlled by the controller 260 which may be a computer thatreceives its commands via DMX 270 from a console 280. The controlling ofthe color correction wheel 220 may include rotating the color correctionwheel to a specified location as described herein.

FIG. 4 shows the transmission characteristics of such a practical, dualpeak suppression filter. The filter has an optical substrate with acoating. The coating has values which are selected to reduce theintensity of the two mid-band mercury peaks without removing all of theenergy in the area which would defeat the purpose of the filter byovercompensating, leaving holes in the spectrum and again, negativelyaffecting the CRI. The filter is also designed to pass those wavelengthsoutside the rejected bands with high efficiency so that the naturalcolor temperature of the beam is minimally affected and the overalllight intensity is not significantly reduced. As can be seen by the peaksuppression filter of FIG. 4, the two peaks of 546.1 nm and 578.2 nm areattenuated by approximately 50%. The area substantially outside of thesevalues, that is areas below approximately 520 nm, and areas aboveapproximately 600 nm are minimally attenuated. For example, theattenuation in those areas may range between 15 and 20%, as comparedwith the 50% attenuation in the desired attenuation areas. Moregenerally, however, the peaks can be at different specific values, andthe coating on the optical substrate can be adjusted to remove thesepeaks. In other embodiments, the amount of removal can be by any amountless than 70 to 80%, but more preferably less than 55%.

FIG. 5 shows the effect of the filter on the arc lamp spectrum of FIG.3. Note that the two peaks have been successfully suppressed and the CRIof the improved spectrum has risen from 75 to 93, a very acceptablelevel. The color temperature has changed slightly since some mercurypeak energy has been attenuated but the change from 5600K to around6200K is a minimal mired shift of −16 MK-1 and still well within what isconsidered the “daylight” range.

Discussion will now focus on the composite color correction wheelaccording to an embodiment. FIGS. 6A and 6B respectively show the lampside (light incident side) and lens side (light exiting side) of a colorcorrection wheel that is intended for correcting the specific highintensity discharge light. However the order of the films does notaffect the overall filtration and final beam color.

Typically, automated luminaires employ circular filter components tocontrol the color and intensity of the projected beam because rotationalmotion is relatively easy to implement and the circular filters take upthe least amount of space. This embodiment is shown as However in somelighting applications, rectangular filter is shown as 220 in FIG. 2.Elements are put into practice and positioned with linear motionactuators controlled by the controller 260 based on local or remotecommands. While the embodiment of FIG. 6A/6B shows a color wheel, thetechniques described herein can be used with any other shape of filterelement. That said, the discussion will focus on the circular colorwheel embodiment.

On the lamp side shown in FIG. 6A, almost the whole surface over thearea 600 is coated with the dual peak suppression filter. There is asector 605 at the bottom of the wheel that is uncoated and meant to passthe unfiltered light beam. The area 605 where the circular beam passesis labeled “Open”. The edges 620, 621 of the suppression filter oneither side of the open position may be patterned with a densitygradient so that the filter edge is not visible in the projected beamwhen the wheel rotates and imparts filtration. If the edge of the filteris hard it could otherwise produce an obtrusive wipe as it moves acrossthe beam.

The lens side of the wheel shown in FIG. 6B is coated with two differentcolor correction filters 630, 640, each residing in two distinct sectorsof the wheel. Coincident with the lamp side, a third sector 650 of thewheel's lens side is left uncoated to pass the “Open” beam. Thisuncoated portion extends in the area 655 beyond the open sector toreveal the underlying peak suppression filter so that it may act aloneon the passing beam.

One of the color correction filters is designed to raise the colortemperature of the beam to a specific value, say 7500 Kelvins shown inthe area 640. The other color correction filter in the area 630 isdesigned to lower the CCT of the beam. The films specifically compensatethe beam color when they are used in conjunction with the peaksuppression film 600 since the two films lie on top of the peaksuppressor 600 shown on the lamp side of FIG. 6A.

Both color correction films 630, 640 are patterned with a densitygradient so that the saturation of the films varies circumferentiallyfrom nothing (zero) to a level producing the desired final CCT.

FIG. 7 shows a portion of a CIE Chromaticity Diagram showing the loci ofthe beam color at different wheel rotation locations. Rotating thecomposite wheel produces the following effect(s) on the output beam ofthe automated luminaire. In the open position the arc lamp beam passesthrough area 605 and 650. The light is unfiltered and, for a typicalcompact HID arc, has a CCT of 5600K with a CRI of only 75 shown in thechromaticity diagram as 0.700. Rotating the wheel in a clockwisedirection (when viewed from the lens side) to the portion with only thepeak suppression filter 655 moves on the chromaticity diagram to raisethe CCT 6500K and the CRI rises to 93, shown as 0.705 in FIG. 7. Therise in CCT and CRI is attributed solely to the suppression of the twomercury peaks.

Thus, the patterning the films creates a saturation gradient that causesthe loci of color correction points caused by the films gradient to liein a straight line. The wheel may be constructed with multiple colorcorrecting filter segments that track the black body curve in apiece-wise manner.

Rotation further in the clockwise direction begins to bring into playthe blue film gradient 640 on the lens side of the wheel which raisesthe color temperature further while preserving the excellent CRI. At theend of the gradient is an area of constant saturation 641 where the beamcolor is 7500K with a CRI of 95 shown as 710 in FIG. 7.

Rotating counterclockwise from the open position 605, 650 graduallyintroduces the temperature lowering amber film 630 which graduallyreduces the CCT. As with the blue film, the amber film has an area ofconstant saturation 631 at the end of the gradient which produces thelowest color temperature of 3000K, for example, with an excellent CRI of87 shown as point 720 in FIG. 7.

FIGS. 8 and 9 show the spectral effects of the composite filtration inthe fully saturated sectors. FIG. 8 shows the arc lamp source's spectrumas curve 800 and, the peak suppression filter's spectral response ascurve 805 in green and the spectral response of the up-converting colorcorrection filter as curve 810. The composite output spectrum of theluminaire is shown as curve 820. Likewise, FIG. 9 shows the compositeeffect of the filtration in the saturated down-correcting sector of thewheel with the light source curve 900, the peak suppression spectralresponse curve 905, up converting correction filter 910 and overallspectral response 920.

These take into account various features. The mercury spectrum peaksuppression filter improves CRI dramatically and raises colortemperature somewhat on its own. The color compensating films shouldthus be designed for taking into account the effect of the peaksuppressor.

The embodiment described above is the preferred embodiment but one ofmany possible implementations of the concepts disclosed. A wheel withmore or less color correction films may be constructed allowingcorrection flexibility to a greater or lesser degree. If more than twocolor correction films are deposited in multiple sectors, a piece-wisecontinuous locus of color points may be constructed which encompasses alonger portion of the Planckian Locus and which also tracks thePlanckian curve more precisely. Since the loci of color points ofvarying saturation are straight lines, one tends to deviate away fromthe black body curve for large excursions of color temperaturevariation. Building a wheel with several coated sectors reduces thelength of each sector's locus in CIE space and thereby its deviationfrom a good CRI. Successive sectors of different patterned filters canproduce a composite locus that stays remarkably close to the black bodycurve thereby preserving Color Rendering Index.

Other embodiments are possible and the inventor intends these to beencompassed within this specification. The specification describesspecific examples to accomplish a more general goal that may beaccomplished in another way. This disclosure is intended to beexemplary, and the claims are intended to cover any modification oralternative which might be predictable to a person having ordinary skillin the art. For example, while this describes certain kinds of highintensity discharge lamps, the techniques described herein can be usedwith other kinds of discharge lamps. Also, while this describes wheels,other techniques of filters can be used.

This system can be used in a stage lighting device, of a type which usesa lamp which produces light, this color correction filter as describedherein, as well as a color and effect producing parts that areconventionally in these lamps, such as gobos and color filters. This canalso be used for example with a zoom lens. The system can be used in aremotely controllable light of a type which is controllable over a linefrom a control console, for example using DMX or some other lightcontrol format. The lamp can be controllable to move to point indifferent directions, for example can be controllable to point in panand tilt.

Both the lamp and the console may be controlled by computers, and thecomputer may control the position to which the filter of the currentapplication is positioned.

The inventor intends that only those claims which use the words “meansfor” are intended to be interpreted under 35 USC 112, sixth paragraph.Moreover, no limitations from the specification are intended to be readinto any claims, unless those limitations are expressly included in theclaims. The system described herein can be controlled by any kind ofcomputer, either general purpose, or some specific purpose computer suchas a workstation. The computers in the lamp may be x86 or Appleprocessors. The computer may also be a handheld computer, such as a PDA,cell phone, or laptop. The computer can be a console that controls theprocessor in the assembly, over a remote control line, e.g. via DMX 512.There may be a user interface that also controls this operation.

The programs may be written in C, or Java, Brew or any other programminglanguage. The programs may be resident on a storage medium, e.g.,magnetic or optical, e.g. the computer hard drive, a removable disk ormedia such as a memory stick or SD media, or other removable medium. Theprograms may also be run over a network, for example, with a server orother machine sending signals to the local machine, which allows thelocal machine to carry out the operations described herein.

What is claimed is:
 1. A color correction filter assembly comprising: anoptical substrate; a first coating on a first surface of said opticalsubstrate, said first coating first attenuating by a first amount bothfirst and second spectral peaks in an optical beam passing through saidoptical substrate, said first amount being greater than a second amountby which areas outside a range including said spectral peaks areattenuated, and where said first attenuating by said first amount is byan amount less than 70% attenuation; and a second coating on a secondsurface of the optical substrate which operates as a color correctionfilter, wherein said first surface of the optical substrate and saidsecond surface of the optical substrate are opposite surfaces of theoptical substrate, wherein said second coating has a first colorcorrection filter property on a first area of the second surface of thesubstrate, said first color correction filter property which raises acolor temperature of the light beam and wherein said second coating hasa second color correction filter property on a second area of the secondsurface of the substrate which lowers the color temperature of the lightbeam.
 2. A filter assembly as in claim 1, wherein said second surfaceincludes an area where there is no second coating, and an edge of saidsecond coating has a density gradient effective to prevent said filteredge from being visible in a beam that passes through the edge.
 3. Afilter assembly as in claim 1, wherein said first and second peakscomprise areas of two mid-band mercury peaks for spectral emission,where said first and second peaks include a first peak above 520 nm anda second peak below 600 nm.
 4. A filter assembly as in claim 3, whereinsaid filters reduce the energy in the areas of said two mid-band Mercurypeaks, without removing all of the energy in said areas.
 5. A filterassembly as in claim 4, wherein said first and second peaks include areacentered around 546 nm and 578 nm.
 6. The filter assembly as in claim 1,wherein said first coating includes a dual peak suppression filter.
 7. Afilter assembly as in claim 6, wherein said optical substrate is in theshape of a wheel, and where said second coating has filter propertiesthat vary on different areas of said wheel.
 8. The filter assembly as inclaim 6, wherein said first coating covers only a portion of thesubstrate, leaving an area of the substrate which does not have thefirst coating thereon and which does not filter light in said area. 9.The filter assembly as in claim 8, further comprising at least onedensity gradient adjacent said area which is left open.
 10. The filterassembly as in claim 6, wherein said second coating includes a firstarea that raises a color temperature of light passing there through anda second area that lowers a color temperature of light passing therethrough.
 11. The filter assembly as in claim 1, wherein said secondcoating includes a density gradient.
 12. The filter assembly as in claim11, wherein said optical substrate is circular, and said densitygradient is along a circumferential direction of the substrate.
 13. Thefilter assembly as in claim 12, wherein said second coating includes anarea of constant density gradient.
 14. The filter assembly as in claim1, wherein said second coating forms a color correction filter that hasa variable color correction filter characteristic, with a first areathat has no coating, a second area in a first direction relative to saidfirst area that raises a color temperature of the beam, and a third areain a second direction relative to said first area that lowers a colortemperature of the beam.
 15. A color correction filter comprising: anoptical substrate, a first coating on an area of a first surface of saidoptical substrate, attenuating by a first amount both first and secondmid-band mercury-created spectral peaks in an optical beam passingthrough said optical substrate, where said first and second peaksinclude a first peak above 520 nm and a second peak below 600 nm, saidfirst amount being greater than a second amount by which areas outside arange including said spectral peaks are attenuated, and where saidattenuating by the first amount reduces the energy in areas of saidfirst and second mid-band mercury peaks, without removing all of theenergy in said first and second areas, where said first coating has thesame filtering characteristic over said area; and a second coating on asecond surface of said optical substrate that has a characteristics thatcarries out a function of a color correction filter that varies acrossdifferent areas of said optical substrate, wherein said first surface ofthe optical substrate and said second surface of the optical substrateare opposite surfaces of the optical substrate, wherein said secondcoating has a first color correction filter property on a first area ofthe second surface of the substrate, said first color correction filterproperty which raises a color temperature of the light beam and whereinsaid second coating has a second color correction filter property on asecond area of the second surface of the substrate which lowers thecolor temperature of the light beam.
 16. A filter as in claim 15,wherein said optical substrate is in the shape of a wheel havingdifferent areas of coating on different areas of said wheel.
 17. Afilter as in claim 15, wherein said first attenuating of said spectralpeaks is by an amount less than 55%, and further operating for secondattenuating of areas outside said range surrounding said spectral peaksby said second amount less than 20%.
 18. A filter as in claim 15,wherein said first and second peaks include area centered around 546 nmand 578 nm.
 19. The filter as in claim 15, wherein said first coatingcovers only a portion of the substrate as said area, leaving an openarea of the substrate which does not have the first coating thereon andwhich does not filter light in said area.
 20. The filter as in claim 19,further comprising at least one density gradient in said first coatingadjacent said area of the substrate which does not have the firstcoating thereon, and an edge of said first coating has the densitygradient effective to prevent said filter edge from being visible in abeam that passes through the edge.
 21. The filter as in claim 15,wherein said second coating includes a first area on the substrate whichraises a color temperature of the light beam and a second area of thesubstrate which lowers the color temperature of the light beam.
 22. Thefilter as in claim 21, wherein said second coating in said first andsecond areas each include a density gradient across said colorcorrection filter.
 23. The filter as in claim 22, wherein said opticalsubstrate is circular, and said density gradient is along acircumferential direction of the filter wherein said second surfaceincludes an area where there is no second coating, and an edge of saidsecond coating has a density gradient effective to prevent said filteredge from being visible in a beam that passes through the edge.
 24. Thefilter as in claim 23, wherein said second coating forms a colorcorrection filter that has a variable color correction filtercharacteristic, with a first area that has no coating, a second area ina first direction relative to said first area that raises a colortemperature of the beam, and a third area in a second direction relativeto said first area that lowers a color temperature of the beam.
 25. Thefilter as in claim 15, wherein said coating includes first and secondcoatings that are on the same surface of the optical substrate.
 26. Acolor correction filter comprising: an optical substrate, having firstand second coatings coated on said optical substrate, said first coatingbeing on a first surface and attenuating by a first amount both firstand second spectral peaks in an optical beam passing through saidoptical substrate over a first area of said substrate, said first amountbeing greater than a second amount by which areas outside a rangeincluding said spectral peaks are attenuated, and where said attenuatingby the first amount reduces the energy of said first and second peaks,without removing all of the energy in said first and second peaks, andsaid second coating being on a second surface and carries out a firstcolor correction filtering on a first area of the substrate which raisesa color temperature of the light beam and a second color correctionfiltering on a second area of the substrate which lowers the colortemperature of the light beam, where both said first and second colorcorrection filtering correct color of an optical beam also passingthrough said first coating, wherein both said first and second coatingscover only a portion of the substrate, leaving an open area of thesubstrate which does not have the first coating thereon and which doesnot filter light in said area, and where edges of both said firstcoating and said second coating that are adjacent to said open area,have a density gradient effective to prevent said filter edge from beingvisible in a beam that passes through the edges, wherein said firstsurface of the optical substrate and said second surface of the opticalsubstrate are opposite surfaces of the optical substrate, wherein saidsecond coating has a first color correction filter property on a firstarea of the second surface of the substrate, said first color correctionfilter property which raises a color temperature of the light beam andwherein said second coating has a second color correction filterproperty on a second area of the second surface of the substrate whichlowers the color temperature of the light beam.
 27. A filter as in claim26, wherein said first and second peaks are first and second mid bandmercury peaks where said first and second peaks include a first peekabove 520 nm and a second peak below 600 nm.
 28. A filter as in claim26, wherein said optical substrate is in the shape of a wheel havingdifferent areas of coating on different areas of said wheel.
 29. Afilter as in claim 26, wherein said first attenuating of said spectralpeaks is by an amount less than 55%, further operating for secondattenuating of areas outside said range surrounding said spectral peaksby said second amount less than 20%.
 30. A filter as in claim 26,wherein said first and second peaks include areas centered around 546 nmand 578 nm.
 31. The filter as in claim 30, wherein said first coatinghas an optical characteristic that is constant across an area of saidsubstrate, and said second coating has an optical characteristic thatvaries across said substrate.
 32. The filter as in claim 31, whereinsaid second coating has a second area in a first direction relative tosaid open area that raises a color temperature of the beam, and a thirdarea in a second direction relative to said open area that lowers acolor temperature of the beam further comprising at least one densitygradient adjacent said area which is left open.
 33. The filter as inclaim 26, wherein said second coating includes a density gradient acrossareas of said first and second color correction filtering.
 34. Thefilter as in claim 33, wherein said optical substrate is circular, andsaid density gradient is along a circumferential direction of thefilter.
 35. The filter as in claim 33, wherein said second coatingincludes an area of constant density gradient of said first and secondcolor correction filtering.
 36. A method of color correction,comprising: on a first surface of an optical filter has a first coating,attenuating a light beam by a first amount both first and secondmid-band mercury-based spectral peaks in an optical beam passing throughsaid optical filter, where said first and second peaks include a firstpeak above 520 nm and a second peak below 600 nm said first amount beinggreater than a second amount by which areas outside a range includingsaid spectral peaks are attenuated, and where said attenuating by thefirst amount reduces the energy in the areas of said first and secondmid-band mercury peaks, without removing all of the energy in said firstand second areas; and on a second surface of said optical filter has asecond coating, also variably correcting a color of the light beam thathas had its first and second spectral peaks corrected by moving theoptical filter in a first direction relative to a reference to increasea color temperature of the light, and moving the optical filter in asecond direction relative to the reference to decrease the colortemperature of the light, wherein said first surface of the opticalfilter and said second surface of the optical filter are oppositesurfaces of an optical substrate forming the optical filter, whereinsaid second coating has a first color correction filter property on afirst area of the second surface of the substrate, said first colorcorrection filter property which raises a color temperature of the lightbeam and wherein said second coating has a second color correctionfilter property on a second area of the second surface of the substratewhich lowers the color temperature of the light beam.
 37. The method asin claim 36, wherein said first attenuating of said spectral peaks is byan amount less than 55%, and said second attenuating of areas outsidesaid range surrounding said spectral peaks is by an amount less than20%.
 38. The method as in claim 36, wherein said first and second peaksinclude areas centered around 546 nm and 578 nm.
 39. The method as inclaim 36, further comprising filtering using an area in said firstcoating which is left open and does not carry out said attenuating saidpeaks.